The present invention relates to a diagnostic system for diesel engines and more particularly to a hardware type and monoboard micro-computer diesel engine fault diagnostic system.
Diesel engines are often used in industrial applications, such as over-the-road trucks or electric gnerating plants. If such an engine stops operating or begins to run poorly, the owner must have it repaired quickly. Otherwise, the malfunctioning equipment may prevent him from running his business. Of course, repairs should also be as inexpensive as possible.
Under one of the more common methods of repairing a diesel engine, a mechanic simply guesses what part or parts of the engine are malfunctioning. The parts are then either replaced or adjusted. If the engine still does not perform properly, the mechanic makes additional guesses and replaces more parts.
This trial and error approach can be expensive if the mechanic guesses wrong and continues to unnecessarily replace operable parts. More importantly, the diesel engine can remain inoperable for extended periods while the mechanic continues to search for the true problem.
Diesel diagnostic equipment does exist that monitors a diesel engine's operation and helps a mechanic identify an engine fault--why the engine doesn't run or runs poorly. Much existing diagnostic equipment, however, is extremely expensive. Moreover, the equipment is complicated and time-consuming to set up and operate.
In addition, much existing diagnostic equipment is too heavy and bulky to be readily transported. Thus, the equipment cannot easily be taken "into the field" and used, for example, on a diesel truck engine that has stalled along the road. Further, most existing devices require the use of special sensors, which must be mounted on or screwed into the diesel engine. Attaching such sensors to the engine may be time-consuming. Moreover, the sensors are expensive and their use may cause the engine to operate differently than it would if the sensors were not attached. As a result, the sensors fail to accurately detect how the engine oprates under normal (non-testing) conditions, and the effectiveness of the diagnostic equipment is decreased.
Each diesel engine includes at least one internal chamber having a vapor within it. When running in a normal, working state, the diesel engine compresses a vapor within the internal chamber and injects a combustible fuel mixture into the chamber. The mixture fires, or explodes, and residual gasses and materials are expelled from the internal chamber.
The movement of parts within the diesel engine that completes such a process defines a working cycle for the diesel engine. The average temperature of the vapor within the internal chamber over a complete working cycle of the diesel engine has, for convenience, given the name "Brake Mean Effective Temperature" by the present inventors.
The present inventors have determined that the brake mean effective temperature is an extremely good indicator of how effectively the diesel engine compresses the vapor within the internal chamber. Moreover, the brake mean effective temperature provides useful data regarding the structural integrity of the diesel engine and its operating characteristics.
Moreover, the internal chambers of many diesel engines include a prechamber and cylinder and a glow plug partially within the prechamber. The glow plug includes an electrically resistive element that may heat up to over 900.degree. centigrade. During the normal, running operation of the diesel engine, a combustible fuel mixture is injected into the prechamber, heated by the glow plug, and ignited.
Under such conditions, the glow plug is an "active" element: it "acts on" the prechamber and fuel mixture, causing them to warm. The present inventors have discovered, however, that the compression and combustion of the fuel mixture also affects the glow plug. Thus, the glow plug can also be used as a "passive" element, where the compression and combustion "act on" the glow plug, affecting its electrical characteristics.
The present inventors have ascertained that by monitoring the electrical characteristics of the glow plugs within a diesel engine, the brake mean effective temperature and other operating characteristics of the engine may be ascertained. Moreover, sensors to monitor glow plugs may be combined with other sensors to form a more inexpensive and portable fault diagnostic system for a diesel engine.